The present invention relates to schottky diodes and, more specifically, to a novel process for their manufacture in which the barrier height is adjusted to a desired value.
Schottky diodes and processes for their manufacture are well known. For example, U.S. Pat. No. 4,206,540 and its divisional U.S. Pat. No. 4,408,216, as well as U.S. Pat. Nos. 4,398,344 and 4,849,199 and application Ser. No. 08/701,847, describe processes for the manufacture of a schottky diode in which a palladium and/or platinum silicide barrier is used as the schottky barrier to a silicon substrate.
An important characteristic of the schottky diode is its barrier height or turn-on voltage, sometimes called its knee voltage. Another important characteristic of a schottky diode is its hot reverse leakage current. Typically, low hot reverse leakage currents are desirable, such as five milliamperes per square millimeter at 125.degree. C.
The known processes for the manufacture of a schottky diode typically attain a barrier height or knee voltage that is fixed and which cannot be changed by the respective process.
For example, a known process for the manufacture of a schottky diode includes a molybdenum to silicon barrier which allows for variations in the resistivity and thickness of epitaxial layer in the upper surface to obtain a targeted blocking voltage and to allow for variations in the die dimensions for targeted current and heat dissipation ranges. The knee voltage for this process is fixed at 0.30 volts.
Another known process for forming a schottky diode uses an ultra-thin palladium-diffused layer formed in the upper surface of the epitaxial layer and upon which a molybdenum film is applied. Such a process is described in U.S. Pat. Nos. 4,206,540 and 4,408,216. The process also allows for variations in the epitaxial layer of resistivity and thickness and attains a targeted blocking voltage with allowed variations and die dimensions for targeted current and heat dissipation ranges. The knee voltage attained using this process is similarly fixed at 0.36 volts.
Though a 0.30 volt or 0.36 volt knee voltage is suitable for many applications, other applications optimally require a schottky diode having other knee voltages and thus require design compromises to use one of the above schottky diodes.
It is therefore desirable to have a process for the manufacture of a schottky diode in which the barrier height can be tailored to the optimal level suitable for a respective application.